@media only screen and (-webkit-min-device-pixel-ratio: 2), only screen and (min-device-pixel-ratio: 2) {
    .replace-2x {
        font-size: 1px;
    }
    .example {
        background-image: url(../images/example2x.png);
        -webkit-background-size:13px 13px;
        -moz-background-size:13px 13px;
        -o-background-size:13px 13px;
        background-size:13px 13px;
    }
}